Power system design criteria for the service continuity of road tunnels

The service continuity of the electrical systems is a fundamental objective for the safety of users in road tunnels, because it assists to prevent accidents and to mitigate their consequences. The black hole effect in the tunnel access area can cause accidents, therefore a support lighting is provided to ensure the perception of any obstacles. In case of fire events, the safety lighting system is essential for the evacuation of users and the ventilation system, in combination with water mist system, is essential to mitigate the effects of fumes and of heat. For lighting and ventilation systems this paper proposes original design criteria for the distribution configuration of the electrical power supply and recommendations for the correct sizing of the power supplies to ensure their continuity of service. The design criteria are based on the partition in modules and zoning of the road tunnels which allow minimizing exposure to thermal stresses from fire (hot scenario) and to mechanical impacts (cold scenario). This paper recommends for the tunnels commissioning the tests of the correct sizing of the power system adequate to overloads and to electrical disturbances, as inrush currents, load imbalances, harmonics, to limit their premature aging and out of service. The road users should receive greater behavioral information on the case of accidents internal to tunnels considering the elevated risk to which they are exposed.